How to get rid of a miscellaneous quest objective in the journal without using setstage

I don't think that there is any additional information in the quest journal about Miscellaneous quests (that is, specifically the quests that get filled under the "Miscellaneous" category in the journal). The one line in the journal is all you get.

(Which, yes, is a surprising choice on Bethesda's part. Most RPGs will give you a paragraph or two about any quest in the journal, but Skyrim seemingly doesn't for Miscellaneous quests.)

However, if you've forgotten the context of the quest (which, as you point out, is very easy to do), you can always turn on quest tracking for that individual quest. Make sure that quest tracking is turned on for the Miscellaneous category as a whole (in the left column), and then turn on quest tracking for the individual quest in the right-hand list. (And maybe turn off quest tracking for other quests.)

Also, don't forget that you can select a Miscellaneous quest and get a map location for that quest.

These will let you at least find the person, place, or thing for that quest, even if you can't recall why or what you need to do with them. In almost all cases, what you need to do becomes clear when you get to the person, place, or thing.

So one more quirk to that, if you want to remove the blood its a bit more complex but do able. Again, follow the first rule of the way of the voice before you do anything.

So as above, open the console (~). Click on the blood stained wall/floor and type markfordelete. Save in a new file, load, and the wall/floor will be missing. Reload your original save file (the one you used before you opened the console) and the wall will be back but the game won't load the quest texture, aka the blood.

It worked for me and my friend, so I hope it works for the rest of you.

-edit- So many quests later, I came back to the house and the bloody walls are back.The trick works to remove them again but it does not appear to be permanent.